An apparatus using an electro-photographic type, for example, a laser printer has a rotatable photoconductive drum and forms an electrostatic latent image by exposing a photoconductive layer on the photoconductive drum by a laser beam from a laser scanning unit after the photoconductive layer on the photoconductive drum is charged uniformly.
In addition, the laser printer is configured to form a toner image by developing the electrostatic latent image by a toner, transfer the toner image on a transfer paper, and then fix the toner image thermally by passing the transfer paper through a thermal fixing device.
Such a conventional thermal fixing device uses a fixing roller including an anti-sticky layer such as fluorine resin to prevent an adhesive of a toner on an outer peripheral surface of a cored bar of a hollow cylinder made of, for example, aluminum, or the like.
The fixing roller is configured to dispose a heater such as a halogen lamp in the hollow cored bar along a rotational central axis of the roller and heat the fixing roller from an inside thereof by radiant heat of the heater.
Furthermore, by providing a fixing roller and a pressure roller contacting with the fixing roller and passing a transfer paper between the fixing and pressure rollers, while melting a toner adhered on the transfer paper by heat of the fixing roller, the toner is transferred on the transfer paper by pressuring. At this time, because the transfer paper is ejected in such a manner that the toner melts and fits closely to the fixing roller, a separating pawl made of a heat-resistant resin such as polyimide, polyamide-imide, PPS (polyphenylene sulfide), or the like is provided to abut with the fixing roller in order to separate the transfer paper from the fixing roller or fixing belt.
In recent, with colorization of images, as a method of fixing a transfer paper in which several colored toners are laminated, a fixing belt including a belt made of a metal or polyimide, an elastic layer of silicon rubber formed on the belt, and an adhesion-preventing layer of a fluorine resin formed on the elastic layer to prevent the adhesion of the toner has been used.
In a fixing belt or fixing roller using a color toner, when the separating pawl is abutted with the elastic layer, the separating pawl bites in the elastic layer there is a problem that the elastic layer, separating pawl or the like is damaged. Therefore, a peeling sheet pr separating plate which does not contact with the elastic layer has bee used.
Conventionally known are various technologies for separating a transfer paper from a fixing member such as a fixing roller or fixing belt.
Japanese Patent Laid-Open No. 2001-83832 discloses a peeling sheet for peeling a recording paper ejected from a nipping part between a fixing roller and a pressure roller from the fixing roller. The peeling sheet is formed from a thin metallic plate and includes an edge having a continuous curvature, and the edge is covered with a coating layer of a fluorine resin having mold-releasing property.
Japanese Patent Laid-Open No. 2002-91222 discloses a peeling member including a supporting member, a peeling sheet connected with the supporting member by a sheet laser spot welding, and a fluorine resin sheet attached to a portion of the peeling sheet close to the fixing roller.
Japanese Patent Laid-Open No. 2004-109636 discloses a separating pawl configured to abut with a fixing roller for contacting with a pressure roller. The separating pawl is disposed so that an angle at which a line connecting centers of the fixing and pressure rollers and a line connecting the center of the fixing roller and a contacting point of the separating pawl with the fixing roller are disposed is set at 40° or less.
In addition, Japanese Patent Laid-Open No. 2003-122175 discloses that when a leading end of a transfer paper passes a separating member contacting with a fixing member, the separating member is moved.
However, in the peeling sheet disclosed in Japanese Patent Laid-Open No. 2001-83832, because the thin metallic plate is bent in a predetermined shape, thereafter the fluorine resin is coated on the bent plate, there is a problem that deformation, bow, damage at a bent portion or the like occurs in the bent plate due to a relatively high baking temperature for the fluorine resin, and therefore a stable gap between the peeling sheet and the fixing roller is not obtained.
Also, in Japanese Patent Laid-Open No. 2002-91222, because the fluorine resin sheet is attached to the peeling sheet by an adhesive, there is a problem requiring some processes such as carrying out a surface treatment such as etching on the peeling sheet, thereafter applying the adhesive to the peeling sheet, after heating and drying it, attaching the fluorine resin sheet to the peeling sheet.
Moreover, in Japanese Patent Laid-Open No. 2004-109636, because the separating pawl contacts with the fixing roller, there is a problem that the separating pawl causes damage to fixing roller.
Furthermore, in Japanese Patent Laid-Open No. 2003-122175, because a moving mechanism to move the separating plate is required, there is a problem that a structure is complicated.